Low-dimensional　perovskite　halides　have　shown　a　great　potential　as　X-ray　detection　materials　because　of　efficient　exciton　emissions　originating　from　strongly　spatially　localized　charge　carriers.　Nonetheless,　most　of　them　have　a　scintillation　yield　far　below　their　theoretical　limits.　Here,　it　is　found　that　the　harvesting　efficiency　of　produced　charge　carriers　can　be　significantly　enhanced　via　a　small　amount　of　In+　doping　in　these　highly　localized　structures.　A　bright　and　sensitive　zero-dimensional　Cs3Cu2I5:In+　halide　with　efficient　and　tunable　dual　emission　is　reported.　The　radioluminescence　emission　of　Cs3Cu2I5:In+　crystals　under　X-ray　excitation　consists　of　a　self-trapped　exciton　emission　at　460　nm　and　an　In+-related　emission　at　620　nm　at　room　temperature.　In+　doping　enhances　the　photoluminescence　quantum　efficiency　(PLQY)　of　Cs3Cu2I5　from　68.1%　to　88.4%.　Benefiting　from　the　higher　PLQY,　Cs3Cu2I5:In+　can　achieve　an　excellent　X-ray　detection　limit　of　96.2　nGy(air　)　s(-1),　and　a　superior　scintillation　yield　of　53　000　photons　per　MeV,　which　is　comparable　to　commercial　CsI:Tl　single　crystals.　As　a　result,　a　remarkable　X-ray　imaging　resolution　of　18　line　pairs　mm(-1)　is　demonstrated,　which　is　so　far　a　record　resolution　for　single　crystal　perovskite-based　flat-panel　detectors.　These　results　highlight　the　importance　of　efficient　harvesting　of　carriers　(and　excitons)　in　low-dimensional　perovskites　for　radiation　detection　applications.